Nephrite Deposits Research Articles

Nephrite from Xinjiang Qiemo Margou Deposit: Gemological and Geochemical Insights

The nephrite belt in the Altun Mountain–Western Kunlun Mountain region, which extends about 1300 km in Xinjiang, NW China, is the largest nephrite deposit in the world. The Qiemo region in the Altun Mountains is a crucial nephrite-producing area in China, with demonstrated substantial prospects for future exploration. While existing research has extensively investigated secondary nephrite deposits in the Karakash River and native black nephrite deposits in Guangxi Dahua, a comprehensive investigation of black nephrite from original deposits in Xinjiang is lacking. Margou black-toned nephrite was recently found in primary deposits in Qiemo County, Xinjiang; this makes in-depth research on the characteristics of this mine necessary. A number of technical analytical methods such as polarizing microscopy, Ultra-Deep Three-Dimensional Microscope, electron microprobe, back-scattered electron image analysis, X-ray fluorescence, and inductively coupled plasma mass spectrometry were employed for this research. An experimental test was conducted to elucidate the chemical and mineralogical composition, further clarifying the genetic types of the black and black cyan nephrite from the Margou deposit in Qiemo, Xinjiang. The results reveal that the nephrite is mainly composed of tremolite–actinolite, characterized by Mg/(Mg + Fe2+) ratios ranging from 0.86 to 1.0. Minor minerals include diopside, epidote, pargasite, apatite, zircon, pyrite, and magnetite. Bulk-rock rare earth element (REE) patterns exhibit distinctive features, such as negative Eu anomalies (δEu = 0.00–0.17), decreasing light REEs, a relatively flat distribution of heavy REEs, and low total REE concentrations (1.6–38.9 μg/g); furthermore, the Cr (6–21 μg/g) and Ni (2.5–4.5 μg/g) contents are remarkably low. The magmatic influence of granite appears to be a fundamental factor in the genesis of the magnesian skarn hosting Margou nephrite. The distinctive black and black cyan colors are attributed to heightened iron content, mainly associated with FeO (0.08~6.29 wt.%). Analyses of the chemical composition allow Margou nephrite to be classified as typical of magnesian skarn deposits.

A New Nephrite Occurrence in Jiangxi Province, China: Its Characterization and Gemological Significance

Nephrite is a very precious gemstone material. As a non-renewable resource, the discovery of new nephrite deposits and the study of the genesis of nephrite have aroused great interest. A new occurrence of nephrite known as Xinyu nephrite was discovered in Xinyu Country, Jiangxi province, China. Field investigations reveal that nephrite appears in a contact zone between the Mengshan composite granitic pluton and Permian carbonate rock. The carbonate rock is calcic marble that underwent diopsidization and tremolitization. Nephrites have a light yellow-green color, weak greasy luster, are slightly-translucent to translucent, and are fine-grained. Their refractive index (RI) ranges from 1.60 to 1.61, and their specific gravity (SG) value ranges from 2.90 to 2.91, falling within the range of nephrites from Xinjiang, China. Their Mohs hardness (Hm) ranges from 5.78 to 5.83. Petrographic observations and electron probe micro analyzer (EPMA) data indicated that analyzed nephrites mainly comprise tremolite, with minor diopside, calcite, quartz, and apatite. Tremolite has a ratio of Mg/(Mg + Fe2+) greater than 0.99. The tremolite grains show microscopic fibrous-felted and columnar textures. Scanning electron microscope (SEM) images show some tremolite fibers interwoven in different crystallographic orientations, and some arranged in parallel. Fourier transform infrared and Raman spectroscopy features reveal the bands of minerals typical for nephrite composition. The petrographic characteristics and geological background of the Mengshan area indicate that nephrite formed through a replacement of calcic marble, which differs from the two known types (D-type: dolomite-related; S-type: serpentinite-related). Mineral replacements were common in nephrite, including diopside by tremolite, calcite by tremolite, and recrystallization of coarse by fine tremolite grains. The discovery of Xinyu nephrite occurrence complements the resource and provides an updated case for the in-depth study of the diversity of nephrite deposits.

Mineralogy and Sr Isotope Characteristics of Dahua Stratified Tremolite Nephrite and Host Rocks, Guangxi Province, China

The tremolite nephrite deposit in Dahua county, Hechi City, Guangxi province, China is a new genetic type of nephrite deposit. It is hosed by Mg-poor limestone (~1.30 wt.% MgO) and intruded by diabase (~45 wt.% SiO2). The Mg and Si contents of these rocks are lower than those of the tremolite (58.18 wt.% SiO2, 13.18 wt.% CaO, 24.16 wt.% MgO), indicating an obviously insufficient source for the metallogenic material that generated the deposit. In particular, some tremolite nephrite ore bodies have no clear contact metamorphism between the host and intrusive rocks, which have the characteristics of stratified mineralization (stratified tremolite nephrite). The origin and mineralization of stratified tremolite nephrite remain poorly constrained. To address this shortcoming, the mineralogy, geochemistry and Sr isotopic of host rock, altered marble, stratified tremolite nephrite and intrusive rock in the Dahua stratified tremolite nephrite deposit were studied. The results show: stratified tremolite nephrite mainly consists of aggregates of microcrystalline-cryptocrystalline tremolites with content exceeding 95%. The in situ rare earth elements (REEs) distribution pattern of hydrothermal calcite in the contact position between stratified tremolite nephrite and marble is similar to that of marine carbonate rock, showing obvious enrichment of HREE, which is different from calcite in limestone and marble. 87Sr/86Sr of stratified tremolite nephrite is relatively uniform, with an average value of 0.7070, within the range of Permian seawater. The mean value of Y/Ho in the hydrothermal calcite is 51.24, indicating that the marine fluid has not been impregnated by terrigenous materials. In summary, the hydrothermal fluid rich in Ca and Si is formed after marine carbonate rocks are altered by marine fluids. Hydrothermal fluids alter diabase rocks formed by altered minerals like titanite, chamosite, zoisite, etc. This process leads to the formation of metallogenic hydrothermal fluids abundant in Si, Ca, Fe and Mg. The metallogenic hydrothermal fluids migrate in faults and fractures of marble and crystallize to form tremolite nephrite under suitable ore-forming conditions.

A New Type of White Nephrite from Limestone Replacement along the Kunlun–Altyn Tagh Mountains: A Case from the Mida Deposit, Qiemo County, Xinjiang, China

The recently discovered Mida nephrite deposit, located in the East Kunlun Mountains, Qiemo County, Xinjiang, Northwest China, contains new types of white and greenish white nephrite formed by limestone replacement, which shows microstructures, macroscopic features and country rocks typologies that are quite different from those of the other deposits along the Kunlun–Altyn Tagh Mountains. The gemological and mineralogical characteristics of Mida nephrite are presented here. These nephrites show an ivory white color and a porcelain-like appearance, with semitranslucent-to-opaque transparency and a porcelain-to-greasy luster. Petrographic study, electron probe microanalysis (EPMA) data and scanning electron microscopy (SEM) images have indicated that the nephrite is composed of tremolite, accompanied by minor quartz, calcite and diopside. Tremolite aggregates have shown different textures, like flaky, granular, fibrous–felted, bundle, radial and metasomatic relict textures. Quartz has appeared in granular or disseminated form, dispersed in the tremolite matrix. Calcite has shown a metasomatic relict texture in the white nephrite samples. Diopside has shown euhedral grains, with some distributed with a certain geometric appearance. Based on our observations, it is suggested that the quartz in the nephrite originated from Si-rich hydrothermal fluids. We propose that the substantial size difference of mineral grains, together with uncompacted grains with inter-particle pores, are the main reasons for the internal reflection and refraction under transmitted light, which allow less transmitted light to pass through the nephrite body and generate the appearance of a semitranslucent-to-opaque transparency, ivory white color and porcelain luster. Our study has unveiled that the Mida nephrite is not typical of the two known types (D-type: dolomite-related; S-type: serpentinite-related) and is overlapped by quartz grains dispersed throughout the less compact tremolite matrix. These observations would help set it apart from the majority of nephrite jades found in the Kunlun Mountains region and provide valuable insights for enhancing comprehension of the diversity of the nephrite deposits.

Understanding Chemical and Mineralogical Composition of Nahartangi Nephrite from Goshta

The geochemical mineralogical characteristics of the Nahartangi nephrite deposit in the Goshta district of Nangarhar province are investigated in this research. Nephrite is a Cyclosilicate mineral with a high silicate content. Ca2(Mg, Fe)5Si8O22(OH)2 is its chemical formula, and it is monoclinic. It's been discovered in metamorphic rocks across the arena. The nephrite zone of Nahartangi is linked to the Jalalabad structural band and the ophiolite complex. Jalalabad is a region in eastern Afghanistan, southeast of Nuristan. As a result, this belt is associated with the upper or late Cambrian. The age of the rocks in this quarter is related to the Archean-Mesoproterozoic AR-PR2. This manuscript offers the first systematic mineralogical and geochemical observation of the Nahartangi nephrite deposit electronic probe Microanalysis, X-ray fluorescence spectroscopy (XRF) and mineralogical analysis. The Nahartangi nephrite was investigated using an XRF and petrographic microscope. According to field research, dolomitic marble is involved in Nahartangi nephrite deposits close to the intrusive granitoids. According to petrographic investigations, nephrite is mostly made up of fine-grained actinolite, schist, and dolomite, all of which are metamorphic minerals. Through every phase, nephrite samples had low Fe/(FeO+MgO) values (8.2524.17%) according to geochemical analysis, and SiO2 (81.30%), Al2O3 (3.22), and CaO (17.41%) were also low and 1.21% NiO content, as well. Chemical records analysis and interpretation of Mg+Fe percentages indicate that actinolite is the type of nephrite. The formation of veins and hydrothermal lenses in contact with serpentinite and carbonates has produced nephrite deposits. Dolomitic marble rocks are the specific rocks found near the study area. The economy and value are immediately impacted by color and its transparency. The presence of Mg elements causes the nephrite from the Goshta district to appear green.

Geochemical Characteristics of Nephrite from Chuncheon, South Korea: Implications for Geographic Origin Determination of Nephrite from Dolomite-Related Deposits

The Chuncheon nephrite deposit in South Korea is one of the major nephrite deposits in the world, but its origin has been rarely studied. This study explores the mineralogical and geochemical characteristics of the Chuncheon nephrite using a polarizing microscope, an electron microprobe, laser ablation, inductively coupled plasma mass spectrometry, and hydrogen–oxygen isotope analyses and compares them with dolomite-related nephrite worldwide. The main mineral of Chuncheon nephrite is tremolite, which has a felted blastic texture, secondary filling texture, and metasomatic pseudomorphic texture that nephrites from other regions do not have. Chuncheon nephrite is dolomite-related; the total content of rare earth elements is generally low, with highly variable positive and negative Eu anomalies and weak positive Ce anomalies; and the light rare earth elements are enriched. The Chuncheon nephrite formed in an anaerobic alkaline environment with a low degree of mineralization, and the hydrothermal fluids are predominantly meteoric water. Nephrite from different regions has different geochemical characteristics as well as different abundances of rare earth element contents. According to the content and range of elements, such as δCe, δEu, ΣREE, (La/Sm)N, and other rare earth elements, dolomite-type nephrite from different origins can be roughly distinguished.

Geochemical characteristics and ore-forming mechanism of Luodian nephrite deposit, Southwest China and comparison with other nephrite deposits in Asia

A nephrite deposit was recently discovered in Luodian, Guizhou Province, which belongs to the South China Plate and is located in the eastern Tethys tectonic domain. This study examines systematically the geochemical characteristics and mineralization mechanism of Luodian nephrite using various analytical techniques including polarized light microscopy, scanning electron microscopy, electron probe microanalysis, and laser ablation-inductively coupled plasma-mass spectrometry. The results show that the main mineral of Luodian nephrite is tremolite, and the secondary minerals include diopside, calcite, quartz, albite, talc, and iron and manganese oxides. The tremolite was present in three morphological forms which have the characteristics of multi-period mineralization. The Mg2+/(Mg2++Fe2+) ratio indicates that the Luodian nephrite deposit is a dolomite-related type deposit. The trace elements of Cr, Ni, and Co, and the ratios of Rb/Sr and Rb/Ba are much lower than those serpentinite-related type nephrite, and are within the range of those for basic magma contact metasomatic nephrite. The rare earth elements (REEs) show that the formation of Luodian nephrite originates from metasomatism of sedimentary rocks. Curves for the distribution of the chondrite-normalized REE pattern and the characteristics of the REEs in nephrite are identical to those for marble or limestone, and are clearly different from those for diabase, indicating that the formation of nephrite occurrs closer to the surrounding rock. Combined with chemical analyses and a geological survey, the results show that Luodian nephrite was formed by the contact metasomatism of basic diabase and carbonate rock during the Indosinian-Yanshannian (Late Triassic to Cretaceous) period. The diabase magma provided a high-temperature environment and the Si hydrothermal environment; the presence of the carbonate rock facilitated Ca and Mg to form nephrite under specific physical and chemical conditions. The comparison of geochemical compositions can help to distinguish the genetic type, reaction mechanism and origin characteristics of nephrite deposits. These results provide theoretical guidance for the search for nephrite deposits of dolomite-related type origin.

Dolomite type nephrite processing wastes and their application

The demand for ornamental stone material has led to an increase in the amount of rock mass being processed. However, the production of lapidary works and jewelry result in a significant amount of waste. This study aims to investigate the material composition and physical and mechanical properties of the solid wastes generated during the processing of dolomite type nephrite in the Vitim region. The accumulation of such waste leads to increased costs of transportation, storage, security, and negative environmental impact. The majority of dolomite type nephrite deposits are located in the Northwest, Northeast, and South of China, in South Korea, Australia, Italy, and Poland, with a large deposit in the Vitim region of Russia. In this study, the waste from the Kavoktinsky deposit, the most productive in Russian, was used. A visual and petrographic examination of nephrite, skarn and amphibolite which are components of the solid waste, was conducted. The macro- and microchemical composition of nephrite of different colors was studied, and X-ray phase analysis was performed. The decorative properties of the waste were determined. A radiation and hygienic certificate was obtained. The waste has a crushability grade of 1200, abrasion grade of I1, and frost resistance of F400. The study has shown that the waste does not contain grains of incompetent rocks, clay, dust, and clay particles. The solid waste form the Vitim nephrite processing is of high quality and meets the requirements of GOST 8267-93, except for an increased content of flagstone (flattened) and large size fragments. It can be used for the production of ordinary, decorative, and mosaic concrete, decorative plates, interior decoration of premises, bathrooms, and saunas, and the manufacture of souvenir products. However, further research is needed to investigate the application of the waste as a raw material for stone casting and a slow-release fertilizer. The utilization of this waste not only solves the problem of waste disposal but also improves economic performance of mineral extraction.

Nyrdvomenshor Nephrite Deposit, Polar Urals, Russia

We studied the quality characteristics, chemical, mineral and isotope composition of nephrite, diopsidite and rodingite of the Nyrdvomenshor nephrite deposit in the Polar Urals. We applied visual petrographic and mineralogical studies, X-ray spectral fluorescence, ICP-MS analysis, and a scanning electron microscope with a dispersive microanalysis system, to measure the oxygen isotope composition. According to its quality characteristics, the nephrite was substandard. Here, uvarovite, which forms idiomorphic grains, sometimes sheath-like and less often xenomorphic elongated, and substituting the chromite, was commonly encountered. The nephrite was formed due to both metamorphic and metasomatic processes. The serpentinite was replaced by diopsidite, which was then replaced by nephrite. The metamorphism intensified the metasomatism of the serpentinite melange and provided the cryptocrystalline tangled-fibrous structure of the nephrite. Then, metamorphism and metasomatism led to the formation of omphacite and the cracking of the nephrite, which reduced its quality. As these processes progressed, the contribution of the crustal fluid increased.

First report of a nephrite deposit from Somaliland, Africa: Characterization and geological and archaeological implications

Nephrite jade is of wide interest, not only for its value as a highly valued precious stone, but also for its significance in tracing geological and petrological processes. Here, we report the first discovery of a nephrite deposit in Africa, located in Somaliland. Field investigations revealed that two open nephrite pits at Goodieood and Laasmacaane are composed of a series of discontinuous vein-shaped nephrite bodies stretching for ∼2 km and defining a nephrite belt. Dolomitic marble and epidote-amphibole are the major rock types in this nephrite belt. Most of the nephrites show grayish green color, while a few are grayish white to light-grayish green, with an occasional brownish rind mainly in nephrite gravels from the secondary deposits. The nephrite is composed of tremolite and actinolite with minor diopside, pargasite, edenite, and apatite. Most nephrites display fine fiber microstructures, and the tremolite-actinolite aggregates show crystallographic preferred orientation. Parallel to the nephrite bodies, epidote-amphibole rocks appear as a metasomatic dark-colored boundary zone, composed mainly of actinolite-tremolite, epidote, and titanite with minor rutile, pargasite, edenite, diopside, and zircon. The dolomitic marble displays dolomite replacement partially by antigorite. Textural observations suggest a sequence from Na-, Al-, and Fe-rich toward Mg-rich compositions, leading to the possibility of prospecting for white nephrite. The various features suggest that the deposit belongs to a fluorine-bearing Ca-Fe-P fluid-dominant skarn. This deposit is estimated to have more than 1000 tons of nephrite jade reserves and has important significance for the exploration for more economic nephrite deposits in Africa, South America, and even Antarctica, as well as potentially important archaeological implications in establishing a connection between the nephrite jades and materials for the Hargeisan lithic industries, as part of the social development in eastern Africa. Comparison with a typical white nephrite deposit in Saidikulam provides insights into the formation of white and nonwhite nephrites.

Spatial-temporal distribution, metallogenic mechanisms and genetic types of nephrite jade deposits in China

The nephrite jade deposits of different tectonic units in China exert significant commercial quality, which have attracted wide attention. However, these deposits have not been systematically summarized to date. Here, we investigate the major nephrite jade deposits in China to decipher their gemological and mineralogical characteristics, spatial-temporal distribution, and mineralization processes as well as to identify their geological settings and gemological properties, via integrating published geochronology, major and trace elements as well as H-O isotopes. The compiled data suggest that the major nephrite jade deposits in China can also be generally divided into green jade-type (GJ-type) and white jade-type (WJ-type) which covers different species, but most of them belong to the latter. The GJ-type nephrite deposits predominantly occur in ophiolite/ophiolitic mélange suites or are embedded into ultramafic serpentine jade orebodies. This type of nephrite jade mainly formed through the late auto-metamorphic metasomatism of serpentine or the spontaneous crystallization/precipitation along suture/shear zones that acted as pathways to migrate Ca-rich fluids during orogeny. In contrast, the orebodies of WJ-type nephrite jade are usually hosted at the contact zones between the dolomitic marbles and intermediate-felsic or mafic intrusive rocks, which were produced through metamorphism-metasomatism during post continent-continent collision, such as the Kunlun orogenic belt with about ∼1,300 km Hetian nephrite belt, and the eastern nephrite jade deposits along the Pacific Ocean. Our study highlights that the nephrite jade deposits in China originally formed during multiple tectonic stages related to the interactions between hydrothermal fluids and metamorphism under subduction accretion- and collision orogenesis-related settings. In addition, this study also provides insights into the genetic discrimination, mineral exploration, and occurrence characteristics of nephrite jade deposits as well as the evaluation and identification of nephrite jade quality.

Petrogenesis of Chatoyant Green Nephrite from Serpentinite-Related Deposits, Ospinsk, Russia: Insights from Mineralogy and Geochemistry

Ospinsk is an area in Russia well-known for mining the highest quality green nephrite in the world. However, the chatoyant green nephrite found here has not been studied to date. This study explores the mineralogy, geochemistry, and petrogenesis of chatoyant green nephrite collected from Ospinsk using polarizing microscope back-scattered electron images, scanning electron microscopy, Fourier transform infrared spectrometry, laser Raman spectroscopy, electron microprobe analysis, and laser ablation inductively coupled plasma mass spectrometry, and compares them with S-type green nephrite from other regions of the world. Tremolite is the main mineral constituent, and chromite, chlorite, graphite, and magnetite are accessory minerals in the samples. The chatoyant green nephrite from Ospinsk is serpentinite-related green nephrite. The Ti content of the chatoyant green nephrite from Ospinsk is significantly higher than that of green nephrite from other places. The chatoyant green nephrite deposit in Ospinsk is a contact metasomatic deposit related to ultramafic rocks. The ultramafic rocks first altered to serpentinite and later converted to tremolite after repeated thermal contact-based metasomatism. During the metasomatism of serpentinite into green nephrite, unilateral, compressive, and shear stresses caused by obduction forced directional growth of tremolite, resulting in chatoyancy.

Polysynthetic Twinning of Diopsides in the Niewang and Tatliksu Nephrite Deposits, Xinjiang, China

Diopside, an important component of the crustal and upper mantle, plays an important role in the formation of nephrite. Polysynthetic twinning in natural diopside, especially from skarns, has rarely been systematically researched. Here, the polysynthetic twinning of natural diopside was investigated in two skarn-type nephrite deposits (Niewang and Tatliksu) in Qiemo, Xinjiang, China. Petrographic observations revealed periodic alternations of dark–light lamellae under cross-polarized light and parallel striations under plane-polarized light, whereas backscattered electron images indicated high homogeneity, which suggested a type of mechanical polysynthetic twinning. According to the optical indicatrix, twins were predominantly oriented as a (100)[100] system. Raman spectra and chemical data show that pyroxenes in nephrite are close to the Di end-member with 0.90–1.04 a.p.f.u. Mg and 0.98–1.05 a.p.f.u. Ca. Both diopside and tremolite from Tatliksu contain slightly higher Fe than those from Niewang. Given the seismic origin of mechanical clinopyroxenes twins, twins of studied diopsides are likely to be attributed to Paleozoic-Mesozoic paleoearthquakes in the Altyn Mountain. A shear stress ≥ 140 MPa and a differential stress greater than 280 MPa are suggested as conditions linked to generation of the twinning of diopsides in the nephrite deposits. The replacement of diopside by tremolite along its twin planes highlights the potential gemological implications, as such replacement by tremolite probably facilitated the formation of dense, fine fibre textures in the nephrites.

Progress on the nephrite sources of jade artifacts in ancient China from the perspective of isotopes

The use of isotopes is crucial for understanding the origin of jade/nephrite. This article first contrasts recent studies on the radioisotopes and stable isotopes of contemporary nephrite deposits in China, Baikal region, and South Korean Peninsula. It then reviews the isotopic analysis of the sources of nephrite artifacts in ancient China, highlighting the concentration of contemporary nephrite deposits with distinct isotopic fingerprints in three significant geographic areas, Northeast Asia, the Yellow River Basin, and South China Region. That is, with regard to Northeast Asia, S‐type and D‐type nephrite in Baikal region, and D‐type nephrite in Chuncheon of South Korea as well as Xiuyan and Kuandian of Liaoning Province can be distinguished well by the radioisotope mineralization age and hydrogen and oxygen isotopic values; with regard to the Upper Yellow River, the isotope method of hydrogen, oxygen and silicon isotopic values has the potential to distinguish the D-type and S-type nephrite in Xinjiang Province and Qinghai Province, while cannot distinguish the D-type nephrite from Hetian, Xinjiang Province and Lintao/Maxianshan, Gansu Province; with regard to South China, the isotope method of the radioisotope mineralization age and hydrogen and oxygen isotopic values has the potential to distinguish D-type nephrite from Fugong in Yunnan Province, Dahua in Guangxi Province and Luodian in Guizhou Province, and S-type nephrite in Hualian, Chinese Taiwan. It is recommended that isotopic database of jade materials from more deposits and excavated jadewares must be established, in order to answer significant archaeological questions regarding the role of jade material utilization in the origin, formation and development of Chinese jade culture and Chinese civilization.

Formation of the Nephrite Deposit With Five Mineral Assemblage Zones in the Central Western Kunlun Mountains, China

Abstract The Saidikulam nephrite deposit, which is famous for its high-quality white nephrite no matter in history and nowadays, is located in the eastern part of the Western Kunlun Orogen, in the northwestern margin of the Tibetan Plateau, Yutian County, Xinjiang, China. Field investigations and petrographic observations revealed the presence of five mineral assemblage zones from granodiorite to dolomitic marble in the Saidikulam nephrite deposit: slightly epidote-altered granodiorite → epidote-altered diopsidite → nephrite → calcite tremolitite → calcite-bearing dolomitic marble. However, little is known about the relationships among these five zones or the formation age of the deposit. The slightly epidote-altered granodiorite consists of plagioclase, orthoclase, quartz, biotite, and epidote, with accessory apatite, zircon, and allanite. They exhibit slightly negative Eu anomalies (0.69–0.72), with declined light rare earth element (LREE) and flat heavy rare earth element (HREE) patterns. They are also strongly enriched in Rb, Zr, U, and Sm and depleted in Hf, Ti, P, and Nb. The epidote-altered diopsidite close to the granodiorite intrusions is a relatively high-temperature metasomatic rock composed of Fe-rich diopside and actinolite, while the calcite tremolitite adjacent to the dolomitic marble is a relatively low-temperature rock composed of prismatic tremolite and calcite. The main mineral component of the nephrite is tremolite, with minor epidote, chlorite, apatite, calcite, graphite, and allanite. The nephrites have low ∑REE contents (4.38–18.53 ppm), with declined LREE and flat HREE patterns. All of the analyzed nephrite exhibits pronounced negative Eu anomalies (δEu = 0.20–0.82), and they are strongly enriched in Rb, U, and Ti and relatively depleted in Ba and HFSEs. SHRIMP U–Pb dating of zircons from the granodiorite yielded a Concordia age of 453.8 ± 3.7 Ma, which is interpreted as the upper limit of the Saidikulam nephrite formation age. The zircons in the epidotized syenite in the deposit yielded a SHRIMP Concordia U–Pb age of 489.2 ± 4.2 Ma. These two ages indicate that the dolomitic marble experienced at least two thermal events. The approximate ages of the nephrite deposits along the giant Kunlun-Altyn Tagh belt indicate that the closure of the Proto-Tethys may have been the predominant driving force for the formation of the whole nephrite deposits. The multistage metasomatism and the Fe absorption of epidote-altered diopsidite had a positive impact on the formation of high-quality nephrite.

Genesis and mineralogical studies of zircons in the Alamas, Yurungkash and Karakash Rivers nephrite deposits, Western Kunlun, Xinjiang, China

Nephrite, an aggregate of fine-grained tremolite or actinolite, is mainly found in Mg-skarn at the contact zone between granitoids and dolomitic marble. The nephrite belt in the southern Western Kunlun Mountains in China is the largest in the world, and includes 11 major skarn deposits and >20 orebodies including the Alamas deposit. In addition, economic placer nephrite deposits occur along the Yurungkash & Karakash Rivers. The nephrite in these deposits contains numerous zircons and some grains have high δ18O values, but the genesis of these zircons is not clear. In this study, we investigated the formation mechanism of the nephrite and origin of zircons in nephrite based on the geochemical and δ18O characteristics of zircons in nephrite from the deposits at Alamas and along the Yurungkash & Karakash Rivers, as well as the CO isotopes of the dolomitic marble at Alamas. We found that zircons in nephrite often occur with tremolite and apatite and the major elements of these zircons are close to those of common magmatic zircon. Zircon grains in the Alamas nephrite are mainly subhedral, 80–130 μm long, 50–90 μm wide, and have clear oscillatory zoning. These zircons have similar REE patterns with Alamas granodiorite, including heavy REE (HREE) enrichment and large positive Ce anomalies (Ce/Ce* = 5.30–368). Such petrographic and geochemical characteristics suggest most zircons are magmatic zircons, with some experienced hydrothermal alteration. Zircon δ18O values in Alamas nephrite are 5.69 ‰–8.85 ‰ (n = 25; an exception of 13.35 ‰), close to those zircons in Alamas granodiorite (6.4 ‰–9.0 ‰) but higher than mantle magmatic zircon (5.3 ± 0.3 ‰). The δ13C (0.79 ‰–1.02 ‰) and δ18O (18.7 ‰–20.6 ‰) values of the Alamas dolomitic marble indicate formation by the partial dissolution of marine carbonate rocks. Zircons in nephrite from Yurungkash & Karakash Rivers deposits are mainly subhedral, 100–160 μm long, 80–30 μm wide, and show clear or obscure irregular zoning. They show HREE enrichment and relatively weak positive Ce anomalies (2.58–35.8), suggesting most zircons have magmatic origin, with some experienced hydrothermal alteration. Zircons from Yurungkash & Karakash Rivers have δ18O values range from 14.6 ‰ to 21.37 ‰ (n = 31; an exception of 9.03 ‰). Irregular baddeleyite grains occur in the nephrite, and fragmented or granular grains occur locally within the nephrite zircons or fissures of zircon. These baddeleyite may have formed via the following reaction between zircon and dolomite: 2Zr[SiO4] + CaMg[CO3]2 → 2ZrO2 + CaMg[SiO3]2 + 2CO2 at 660–710 ℃ and 3 kbar. In Yurungkash & Karakash Rivers nephrite deposits, considering these placer nephrite come from Mg-skarn, these high δ18O zircons probably have initially formed within endoskarn, close to the margin of the granitoid where marble with high δ18O was assimilated into the melt, and retain nice oscillatory and/or sector zoning.

Mineralogy and Geochemistry of Nephrite from Wolay Deposited, Kunar, East Afghanistan

This research deals with the study of geochemical, petrographic and mineralogical properties of Wolay Nephrite Occurrences in Kunar Province. Nephrite is a relatively silicate mineral, Cyclosilicate, with a chemical composition of Ca2(Mg,Fe)5Si8O22(OH)2 and has a monocline crystal shape. It is found in metamorphic rocks in many parts of the world. Wolay nephrite area is related to the tectonic zone of Jalalabad. Jalalabad zone is located in the eastern part of Afghanistan and south-east of the Nuristan zone. Correspondingly, this zone is related to the upper Cambrian or younger Cambrian. In this area, the age of rocks is related to Archean- Middle Proterozoic AR-PR2. This contribution presents the first systematic mineralogical and geochemical studies on the Wolay nephrite deposit. Electron probe microanalysis, X-ray fluorescence (XRF) spectrometry, inductively coupled plasma mass spectrometry (ICP-MS), and isotope ratio mass spectrometry was used to measure the mineralogy, bulk-rock chemistry, and stable (O and H) isotopes characteristics of samples from Kunar. Field investigation shows that the Kunar nephrite ore body occurs in the dolomitic marble near the intruding granitoids. Petrographic studies indicate that the nephrite is mainly composed of fine-grained actinolite with Schist and dolomite. Geochemical studies show that all nephrite samples have low bulk-rock Fe/(FeO + MgO) values (4.72–21.34%), as well as SiO2 (72.75%), Al2O3 (2.01), CaO (14.58%) and NiO (0.05%) contents. The chemical data analysis and interpretation of F=Mg/Mg+Fe percentages show that the Nephrites type is actinolite. The deposit of nephrite mineral has been formed in hydrothermally veins and lens shape in contact with serpentinite and carbonate (dolomite marble) rock in the under study area. The color and its clarity have a direct effect on the economy and its price. The Nephrite from the Khas Konur district is found in green color due to the existence of iron elements.

Origin of the subduction-related Tieli nephrite deposit in Northeast China: Constraints from halogens, trace elements, and Sr isotopes in apatite group minerals

Apatite, which is an excellent tracer of geological processes and magma evolution, can record a variety of information about melt and/or ore-fluid evolution by incorporating large amounts of trace elements. In this study, we conducted an in situ geochemical analysis of apatite from the Tieli nephrite deposit in Northeast China and evaluated the genetic mechanism along with the source. The apatite from the Tieli nephrite deposit in Northeast China is magmatic apatite characterized by positive Ce anomalies, negative or positive Eu anomalies, enrichment in light rare earth elements, depletion in heavy rare earth elements, and high F content. The apatite coincides with plagioclase crystallization with positive Sr-(La/Yb)N/(Sm/Yb)N correlations. The geochemical characteristics of the redox-sensitive elements (Eu, V, As, and Mn) in apatite indicate that the parental magma has a high oxygen fugacity between HM (Hematite–Magnetite) and NNO (Ni-NiO). The estimated F and Cl contents of the source area (average values of 1694 and 2328 ppm, respectively) are higher than the average values of the continental crust and primitive mantle, indicating a convergence process of halogens in the source area. The non-chondritic Y/Ho ratios of the apatite (3.34–53.64) imply that the magma interacted with a high volume of fluids. Combined with the findings of previous studies, the 87Sr/86Sr values in apatite suggest contributions from crust and mantle materials. Moreover, the positive correlation between Sr and 87Sr/86Sr may indicate that the subducted sediments altered by seawater were added into the magma chamber. Based on the above findings, the subduction of the Pacific Plate may supply source material and power for magmatism and mineralization in the Tieli nephrite deposit.

A new model for the formation of nephrite deposits: A case study of the Chuncheon nephrite deposit, South Korea

The Chuncheon nephrite deposit is the largest in South Korea with an estimated reserve of 300,000 tons. Located in mid-eastern South Korea, the deposit is in the form of lenses in the contact zone between dolomitic marble and amphibole schist in the upper part of a biotite schist. To date, the origin, process of formation, and age of the Chuncheon nephrite deposit remain unclear, which hinders our further understanding of the formation of nephrite. This study involved petrography, chemical analyses, and nephrite age determinations using optical mineralogy, electron microprobe-analyses (EMPA), X-ray fluorescence spectroscopy (XRF), and SHRIMP (Sensitive High-Resolution Ion MicroProbe) analyses of zircon. Petrographic studies indicated that the Chuncheon nephrite consists mainly of tremolite. The low contents of Cr (2.15–4.74 ppm) and Ni (2.95–4.90 ppm) are typical of dolomite-related nephrites and lower than in serpentine-related nephrites. The total REE contents are <18.5 ppm. The REE chondrite-normalized patterns display right-leaning LREE and almost flat HREE patterns, which are consistent with the REE model of dolomitic marble. The δ18O isotope compositions of the zircons (6.34‰–12.5‰) from the nephrite overlap those of the Chuncheon dolomite (2.4‰–18.2‰), indicates clearly that dolomite played an important role in the formation of the Chuncheon nephrite. The petrography and geochemistry suggest that it had a metasomatic origin involving the reactions dolomitic marble → diopside, diopside → tremolite, and tremolite → chlorite. The δD and δ18O isotope compositions of our specimens of nephrite (δD = − 95.3‰ to − 78.3‰ and − 118‰ to − 105‰; 18O = − 9.9‰ to − 7.9‰) and the hydrothermal fluids in equilibrium with the nephrite (δD = − 73.6‰ to − 56.6‰ and − 96.3‰ to − 83.3‰, 330–450 °C; δ18O = − 9.41‰ to − 6.38‰, 330–430 °C) suggest that the hydrothermal fluids were predominantly meteoric water. The zircons contain almost no mineral inclusions, which is quite different from zircons in other nephrite deposits. The variable SHRIMP U–Pb ages of the zircons (908.9 ± 4.8 to 459.1 ± 1.9 Ma (n = 7), 436.3 ± 16.9 to 359.5 ± 6.4 Ma (n = 5), and 249.9 ± 5.2 to 79.4 ± 1.9 Ma (n = 5)) in the Chuncheon nephrite may record the ages of a regional multi-stage metamorphism. Due to the generally low temperature of formation of the nephrite, we speculate that the ages of zircons only record the two relatively high-temperature initial stages of nephrite formation (dolomitic marble → diopside, and diopside → coarse-grained tremolite) and failed to record the age of the lowest-temperature third stage of high-quality nephrite formation (coarse-grained tremolite → fine-grained tremolite). It has generally been considered that dolomite-related nephrite forms at the contacts between granite/granodiorite and dolomitic marble, whereas serpentinite-related nephrite forms at the contacts between serpentinite and silica-rich rocks. However, the genesis of the Chuncheon nephrite deposit does not fit with either of these well-known types. Thus, we developed a new model for the Chuncheon nephrite in which heat was provided by regional multi-stage metamorphism, meteoric water dominated the nephrite-forming fluids, and dolomitic marble and biotite schist provided the material for the nephrite.

Overview of Gemstone Resources in China

Gemstones are minerals of gem qualities used for adornment and decoration with the attributes of beauty, durability and rarity. Traditionally, although China has been regarded as the most important source for nephrite, over the past decades, a large variety of gemstone resources have been newly discovered in China owing to continuous exploration works. The vast land with various geological and geochemical backgrounds is rich in gemstone resources with potential for new deposits discoveries. In pegmatites, gemstones are related to granitic magma events and mainly occur in pegmatitic cavities, such as tourmaline, aquamarine, spodumene, spessartine, moonstone, quartz, apatite, and topaz. The eruption of Tertiary basaltic magma provides gem-quality sapphire, spinel, olivine, garnet, and zircon. The supergene oxidation zones of some copper and iron deposits in Hubei and Anhui province host gem-quality turquoise and malachite. Moreover, the formation of the nephrite deposit in China is mostly related to the carbonatite and serpentinite rocks involved in the metamorphic-metasomatic processes. This paper comprehensively introduces the distribution of gemstones deposits, as well as the gemological and mineralogical characteristics of gemstones in China. Our present investigation provides insights into the gemstone potential of China for further exploitation.